Hydrocarbon conversion process



Aug. 7, 1945. w. A. scHuLzE .rs1-Al.`

' HYDROCARBON CONVERSIO`v PROCESS Filed June 14, 194s' Patented Aug. 7, 1945 i UNITED STATES HYDROCARBQN QONVERSION PROCESS Walter A. Schulze and Jesse A. Guyer, Bartlesville, Okla., assignors to Phillips Petroleum Company, a corporation of Delaware Application June 14, 1943, Serial No. 490,820

Claims.

This invention relates to the production of aromatic hydrocarbons from petroleum hydrocarbons of predominantly non-aromatic character. In one specific aspectl it involves the production of gasoline stocks of high aromatic content vval-` uable both as aviation gasoline blending agents and as sources of pure aromatic hydrocarbons. Still more specifically, this invention embodies a novel combination of non-catalytic and catalytic conversion steps for the conversion of light hydrocarbon gases and naphtha-type liquid hydrocarbon charge stocks into predominantly aromatic gasoline-type liquid products.

One object of" this invention is the production of aviation gasoline stocks of high aromatic content and superior rich mixture combustion characteristics.

Another. object of this invention is the more efficient and complete-aromatization .of predominantly aliphatic hydrocarbons.

Still another object of the invention is to provide a two-stage process for the production of -aromatic hydrocarbons in the gasoline boiling range utilizing the most efficient features of noncatalytic and catalytic conversion operations.

These and other objects such as the production of pure benzene and/ or toluene, the utilization of light olefins from both stages of the process to produce additional liquid feed stock for the catalytic treatment, and the improved method of performing catalytic aromatization will be apparent'from the following disclosure.

The production of aromatic hydrocarbons or of gasoline stocks containing large proportions of aromatic compounds from petroleum oils and gases is of particular importance because of the increasing requirements for aromatics in numerous chemical syntheses and for higher quality aviation fuels. Various methods for accomplishing the conversion of aliphatic or naphthenic hydrocarbons to aromatics have been proposed, and have, in general, involved either non-catalytic cracking under severe temperature conditions or catalytic treatment of carefully selected stocks at much lower temperatures. 'I'he rsttype of process has usually yielded aromatic oils as asmall volume by-product of fuel gasproduction. The second type of process hasproduced more favorable yields of liquid products, but with generally limited aromatic concentrations.

In the `operations producing aromatics by thermal 'or non-catalytic treatment of either normally gaseous or liquid hydrocarbon mixtures,

55 carbon formation is not detrimental; and (2) temperatures of about 1300* to about 1600 F. are

often named, with lowpressures and very short reaction time. Under these conditions, aromaticforming reactions are accompanied by deep conversion to dry gas (methane and ethane) tar Y and carbon, and process economics may depend on the value of the fuel gas, carbon black. and other recoverable products. The light liquid products may be almost entirely mixtures of aromatic hydrocarbons but represent small yields on the basis of the charging stocks. Such thermal processes also usually require special equipment because of the temperatures employed and the carbon and coke formation, so that equipment employed for conventional petroleum refining processes is not easily adaptable.

When aromatization is attempted by catalytic treatments of liquid hydrocarbon stocks, there have heretofore been limitations on the extent of conversion, and, hence, on the concentrations of aromatics in the products. While certain naphthenes may be converted by dehydrogenation to the corresponding aromatics in`high yields, the volumes of such special stocks which are available are obviously limited. When aromatization p of predominantly aliphatic hydrocarbons is attempted in a single catalytic treatment, the aromatic-forming reactions usually must take place under the same conditions (time, temperature, etc.) which produce the olenic or other aromatic-forming intermediates. Since the aromatic-forming reactions are generallyv favored by dieren't reaction conditions, the extent of said reactions may be relatively minor. If, on the other hand, optimum aromatic-forming conditions are employed, there is excessive destruction of charging stocks wi-th resultant high pro- A duction of dryv gas and carbon. Carbon deposition alone may introducev such difcultiesl in.

catalyst reactivation that satisfactory catalytic operation is not feasible.

We have now discovered an improved and more efficient process for the production of aromatic hydrocarbons from predominantly aliphatic charging stocks which results in both improved yields of valuable products and in much higher concentrations of aromatic hydrocarbons in the'A gasoline boiling range than have heretofore been achieved by catalytic means. volves two basic operations as follows: 1) a noncatalytic treatment of mixed gaseous and liquid hydrocarbon charge stock to produce relatively refractory olenic and/or'cyclic intermediates for aromatic formation'under conditions such that catalytic treatment of the intermediate liquid stock under optimum conditions for aromatic formation.

This process will be explained in detail with reference to the drawing which is a schematic flow diagram of process operations.

According to the drawing, fresh Cri-C4 mixed feed is mixed with recycle feed of similar composition and passes through lines I and II to furnace I2. The normally gaseous hydrocarbon charge is heated in a coil in furnace I2 at temperatures of about 1000 to 1100 F. and pressures of about 1500 to 2200 pounds gage for a time producing the desired degree of conversion to normally liquid products. A naphtha charge supplied by line I3 is simultaneously heated to temperatures of about 950 to 1050 F. and injected into the soaking coil containing the reaction mixture from the gaseous feed, and the combined streams undergo further conversionv before exiting through line I4. Quick temperature reduction is effected by injection of cold quench oil from line I5, and the partially .cooled stream passes to high pressure tower (separator and fractionator) I6. This tower is operated under conditions such that an unstripped gas stream comprising C3 and lighter gases is removed through ,line I'I. Heavierproducts are taken through line I8 to stabilizer I9 wherein C4 and lighter hydrocarbons are removed overhead -by way of line 20.

The light hydrocarbons in line pass through a condenser to accumulator 2I. Uncondensed gases pass through line 22 to join' gases from tower I6. .Liquid condensate is removed through line 23 either for reflux `or for recycle to the process. The combined unstripped gas streams (I1 and 22) pass to absorber 24 for stripping of C3 and C4 components. The stripped gas is taken through line 25 to other uses, while C3 and C4 hydrocarbons, together with condensate from line 23 are recycled through line 26.

Pressure distillate from the bottom of tower I9 passes to column 28 for fractionation into gasoline of about 400 F. end point'and heavier bottoms. The gasoline then is taken through line 30 to column 3I where a light gasoline fraction may be removed vthrough line 32. The fractionation in column 3l may be operated to produce any desired initial boiling point in the heavier gasoline bottoms product. For example, C5 hydrocarbons may be separated as of little value in subsequent stages of the process. In some cases Ce hydrocarbons may also be separated without, however, any removal of benzene y from the bottoms product.

charge stock and the liquid naphtha in the same reaction zone enables much higher recovery of liquid products in the gasoline boiling range from the first stage naphtha conversion. The combination of the liquid products from the naphtha and from the light gas conversion produces a stock of particular value for catalytic conversion to `aromatics because of its refractory nature and high concentration of aromatic-forming compounds. At the same time, the relatively deep 5I vis taken through line 53 and may be used moved, through line 41.

rst stage conversion is accomplished without excessive formation of dry gas 4and carbon.

The gasoline charge to the catalytic treatment passes through line 34 to furnace 35 where it is preheated, mixed with superheated steam from line 36, and brought rapidly to conversion temperature in the range of about 1050 to 1200 F. The vapor mixture then passes through line 31 and catalyst chamber 38 containing an. aluminabase catalyst. The catalytic treatment is conducted under low super-atmospheric pressures usually of about 50 to 250 pounds gage. Contact times and Ilow rates are adjusted to conform to the desired degree of conversion.

The eluent vapors from catalyst case 38 pass through' line 39 and waste heat boiler 40 for rapid temperature reduction'. The partially cooled vapors then pass through lines 4I and 42 to separating and fractionating equipment. Two catalyst chambers 38 and 38a with corresponding auxiliary equipment are shown, although more may be provided to give continuous processing while temporarily spent catalyst is being reactivated by combustion of the carbonaceous deposits accumulated during the conversion step.

The reaction products pass first through separator 43 where small quantities of heavy tar or high-boiling residuum are removed through line 44. The vapors pass through line 45 and a condenser to accumulator 46. Water may be re- The hydrocarbons then pass through line 48 to stabilize'r 49 Where lowboiling components are removed. The vapors taken overhead through line 50 pass through a condenser to accumulator 5 I.

Uncondensed gases from 5I are taken through line 52 to absorber 24 for recovery of the C3 and C4 hydrocarbons. Condensate from accumulator` partly for reflux while the remainder passes through line 54 to the rst stage absorber for recycling to the first stage conversion where the Cs and C4 paralins and olens produce additional gasoline charge to the catalytic stage.

Alternately, accumulator 5I may be operated so as to send C3 and lighter hydrocarbons to the first stage absorber while C4 and/or C5 hydrocarbons which are rich in olefins are sent to alkylation unit 55. Isoparaflin stocks maybe added from line 56 for the alkylation operation producing aviation alkylate gasoline.

The stabilized gasoline from the bottom of column 49 passes through line 51 to unit- 58 where clay treatment or the like for improving color and eliminating gum-forming components is performed. The treated gasoline then is fractionated in equipment indicatedby unit 59 for the segregation of the desired products. This fractionating equipment may, for example, produce a benzene concentrate, light aviation gasoline, and heavier fractions suitable for motor gasoline. Pure benzene and toluene may be obtained by suitable purification or extraction of the respective concentrates.

With preferred charge stocks to the catalytic treatment, high yields of liquid products are obtained at the conversion conditionskproducing maximum concentrations of aromatic hydrocarbons. Steam present in the gasoline charge reduces coke formation in the preheating furnace and also reduces carbon deposits on the catalyst. The aromatization reactions are exothermic, so that there is ordinarily a temperature rise in the vapors during passage through the catalyst. More precise temperature control may be ob- 'to the absorber.

' plication. However, no limitation to the feed stocks on the specific operating conditions is implied. r

`A mixture of approximately 80 per cent propane and 20 per cent butane was employed as fresh gas charge to a naphtha-gas reversion opin the gasoline boiling rangeA and Weight per cent as Ca-C4 recycle stock. The olen content of the Ca-C4 stock was over 'l0 per cent. Fractionation of the gasoline gave an aviation gasoline fraction amounting to about GOgWeight per centof the charge and containing approximately 70 weight per cent of aromatic hydrocarbons.

eration along with the recycle Ca-C4 mixture obtained in process operations. The gas charge was treated in passage through two sections of a furnace coil at'an inlet temperature 1070 F. and 2600 pounds gage pressure. The outlet coil temperature was 1010 F. A naphtha charge stock was injected into the second or soaking section ofthe coil at 970 F. This naphtha was a mixture of straight run and cracked stocks of 100- 400 F'. boiling range, and approximately equal volumes of light gas feed and naphtha on a liquidliquid basis were charged to the unit.

The furnace eiliuent was cooled by injection of cold oil, and light gases were separated in two steps. A predominantly Ca and lighter gas fraction from the first step was passed to an oil absorption unit for propane-propylene recovery.

The second step was stabilization to remove C4 and lighter material, this C4 and lighter material being condensed, and the uncondensed gas going A portion of the condensate was used to reflux the C4 and lighter stabilizer column while the excess liquid was recycled to the furnace along with Ca and C4 hydrocarbons obtained from the absorber.

The liquid stabilizer -bottoms product was fractionated to separate the portion boiling above about 400 F., and the gasoline obtained was topped in a subsequent operation to produce an initial boiling point of about 160 F. 'I'he resulting gasoline had a gravity of 51 A. P. I., a bromine number of about 50 and contained a high percentage of cyclic hydrocarbons including about three weight per cent each of benzene and toluene.

This gasoline was charged to the second stage catalytic treatment after preheating and mixing with superheated steam in the weight ratio of '6:1.

12-20 mesh granular bauxite catalyst. The charge rate was 1.2 liquid volumes of gasoline per volume of catalyst per hour and the treating pressure was 85 pounds gage. An average upward temperature gradient of about 60 F. was maintained through the catalyst bed.

The catalyst chamber effluent was passed through a waste heat boiler and after partial coolwhile excess Cs-Ctreflux liquid was added to the recycle gas feed to the first stage conversion.

vThe gasoline was clay treated and refractionated to produce an aviation gasoline fraction in the boiling range ofv 200-330 F., a benzene concentrate and the remaining fractions boiling above and below the aviation stock were combined as n high octane motor fuel.

The oil-steam mixture was then rapidlyvheated to l090 F. and passed through a bed of In an alternative product recovery operation on .the catalytic product stream, C3 hydrocarbons were returned to the rst stage as recycle feed while C4 and C5 hydrocarbons were utilized in alkylation units with isobutane to produce aviation alkylate. The aviation gasoline fraction was prepared with a boiling range of 160330 F. to contain the benzene fraction, andthe lower and higher boiling fractions were combined as motor fuel.

While the natural mineral catalyst bauxite is preferred in many applications of the abovedescribed catalytic treatment, other natural or synthetic alumina-base contact catalysts may be employed. Bauxite and the other preferred catalysts are characterized by rugged physical properties and resistance to poisoning or deterioration by sulfur compounds, repeated reactivation at temperatures up to `about 1500 F., and use in the presence of large proportions of steam. Either bauxite or synthetic alumina catalysts may be composited or impregnated with other metal oxides which are stable at operating temperatures and-Which may accelerate aromatization reactions and/or suppress coke deposition. The oxides or hydroxides of magnesium and the alkali or alkaline earth metals are employed in certain instances in minor proportions.

As indicated above, particular process eiiiciency is obtained by the steps of the process whereby the primary conversion is accomplished with high yields of desirable liquid products but without troublesome carbon and dry gas formation. As a result of the primarynon-catalytic treatment, a stock of superior characteristics is provided for the catalytic. treatment, so that aromatization reactions can be conducted under optimum conditions and with enhanced yields and concentra-v tions of aromatic hydrocarbons in the products. We claim:

. l. A process for the production of gasolin stocks of high aromatic content which comprises heating a C3-C4 hydrocarbon stream, admixing this heated Cri-C4 hydrocarbon stream with a previously vaporized and heated naphtha and subjecting the mixture to a thermal cracking treatment, separating the thermal conversion eiliuent into at least a Css-C4 hydrocarbon fraction, alight gasoline fraction and a heavier gasoline fraction, and recycling the C3-C4 fraction into the original Ca-C4 hydrocarbon stream; subjecting the said heavier gasoline fraction to a catalytic cracking treatment under aromatizing conditions, separating the catalytic conversion eiliuent into at least a Ca-C4 hydrocarbon fraction and a gasoline Reaction products from the catalytic treatment y includedabout flo weight per cent of the charge fraction of high aromatic content, and recycling the latter Cs-C4 hydrocarbon fraction into the original Csi-C4 hydrocarbon stream.

2. A process for the production of gasoline` stocks of high aromatic content which comprises heating a C3-C4 hydrocarbon stream, admixing this heated hydrocarbon stream with a previously vaporized and heated naphtha of approximately to 400 F. boiling range and subjecting the mixture to a thermal cracking treatment, sub- .lecting the thermal conversion eiiluent to a quenching step, and separating said quenched conversion eiiiuent into at least a (Ja-Chhydrocar bon fraction, a light gasoline fraction and a heavier gasoline fraction having a boiling range of substantially 160 to 400 F., and recycling the Ca-C4 fraction into the original Ca-C4 hydrocarbon stream; subjecting the said heavier gasoline fraction in the presence of steam to a catalytic cracking treatment under aromatizlng conditions, separating the catalytic conversion effluent into at least a Ca-Ci hydrocarbon fraction and a gasoline4 fraction-of high aromatic content, and recycling the latter C3C4 fraction into the original Cia-C4' hydrocarbon stream.

3. A process according to claim 2, in which the vgasoline fraction of high aromatic content is further fractionated to produce an aviation gasoline fraction having a boiling range of about 200 to 330 F. and a benzene concentrate.

4. A process according to claim 2, in which the gasoline fraction of high aromatic content is further fractionated to separate an aviation gasoline fraction containing benzene and boiling in the range of 160 to 330 F., and fractions boiling above 330 F. and below 160 F. and combining these higher and lower boiling fractions as motor fuel.

5. A process for the production of gasoline stocks of high aromatic content which comprises subjecting a Ca-C4 hydrocarbon stock to thermal conversion at a temperature within the approximate range of 1000 to 1100 F., and at a pressure within the approximate range of 1500 to 2200 pounds per square inch, and while at said temperature and pressure conditions adding to the heated C a-C4 hydrocarbon charge a vaporized stream of naphtha preheated t a temperature within thel approximate range 950 to 1050 F., and maintaining said combined feed at thermal conversion conditions for a relatively short period of time, subjecting the thermal conversion ellluent to a quenching step, and separating the quenched stream into at least a Cs-C4 hydrocarbon fraction, a light gasoline fraction and a heavier gasoline fraction, and recycling the C3-C4 fraction with the original C3-C4 hydrocarbon charge; vaporizing Vand preheating said heavier gasoline stream, adding steam to said preheatedheavier'gasoline and rapidly heating the combined stream to a temperature within the approximate range of 1050 to 1200 F., subjecting the heated stream to catalytic conversion under aromatizing conditions within said approximate temperature range at a pressure within the approximate range of 50 to 250 pounds per square inch, rapidly cooling the catalytic conversion ellluent, and separating the cooled effluent into at least a C11-C4 hydrocarbon fraction and a gasoline fraction of high aromatic content,` and recycling the latter Caf-C4 hydrocarbon fraction into the original C3C4 charge stock.

6. A process as defined in claim 5 wherein the catalyst is an alumina-base catalyst.

7. A process as defined in claim 5 wherein the catalyst is a bauxite catalyst.

8. A process as dened in claim 5 wherein the catalyst is a synthetic alumina catalyst.

9. A process for the production of gasoline stocks of high aromatic content which comprises subjecting a C3-C4 hydrocarbon stock to thermal conversion at a temperature within the approximate range of 1000 to 1100 F., and at a pressure within the approximate range of 1500 to 2200 pounds per square inch, and while at said temperature and pressure conditions adding to the heated Cs-C4 hydrocarbon charge a vaporized .stream of naphtha preheated toa temperature Within the approximate range 950 to 1050 F.,

'maintaining said combined feed at thermal conversion conditions for a relatively short period of time, subjecting the thermal conversion eiiluent to a quenching step, separating the quenched stream into at least a C3-C4 hydrocarbon fraction, a light gasoline fraction and a heavier gasoline fraction, and recycling the C3-C4 fraction with the original .C3-C4 hydrocarbon charge; vaporizing and preheating said heavier gasoline stream, rapidly heating the stream to a temperature within the approximate range of 1050 to 1200 F., subjecting the heated stream to catalytic conversion under aromatizing condtions within said approximate temperature range at a pressure within the approximate range of 50 to 250 pounds per square inch, rapidly cooling the catalytic conversion eilluent, separating the cooled eflluent into at least a Ca-C4 hydrocarbon fraction and a gasoline fraction of high aromatic content, and recycling the latter Ca-C4 hydrocarbon fraction into the original Cs-Ci charge stock.

10. A process for the production of gasoline stocks of high aromatic content which comprises subjecting a, Ca-C4 hydrocarbon stock to thermal conversion at a temperature within the approximate range of 1000 to 1100 F., and at a pressure within the approximate range of 1500 to 2200 pounds per square inch, and while at said temperature and pressure conditions adding to the V heated C3C4 hydrocarbon charge a vaporized stream of naphtha having a boiling range of about -400 F., preheated to a temperature within the approximate range 950 to 1050 F., maintaining said combined` feed at thermal conversion conditions for a relatively short period of time,

subjecting the thermal conversion eilluent to a quenching step, separating the quenched stream into at least a C3-C4 hydrocarbon fraction, a light gasoline fraction and a heavier gasoline fraction,

having a boiling range of about -400 F., and recycling the Cai-C4 fraction with the original (2a-C4 hydrocarbon charge; vaporizing and preheating said heavier'- gasoline stream, rapidly heating the stream to a temperature within the approximate range of 1050 to 1200 F., subjecting the heated stream to catalytic conversion under aromatizing conditions within said approximate temperature range at a pressure within the approximate range of 50 to 250 pounds per square inch, rapidly cooling the catalytic conversion eiiluentl separating the cooled eflluent into at least a Ca-C-i hydrocarbon fraction and a gasoline fraction of high aromatic content; substantially boiling inthe range of 160-330 F., and recycling the latter Ca-C4 hydrocarbon fraction into the original C3-C4 charge stoc WALTER A. SCHULZE.

JESSE A. GUYER. 

